private static void printDigests(JChannel[] channels) {
for(JChannel ch: channels) {
NAKACK nak=(NAKACK)ch.getProtocolStack().findProtocol(NAKACK.class);
Digest digest=nak.getDigest();
System.out.println(ch.getName() + ": " + digest.toStringSorted());
}
}
static void waitForNumMessages(int num_msgs, long timeout, long interval, MyReceiver ... receivers) {
long target_time=System.currentTimeMillis() + timeout;